The present invention relates generally to poppet valves for internal combustion engines, and more particularly, to a hollow poppet valve which is able to maintain a very high strength-to-weight characteristic. Although the present invention is adapted for use with many different types of hollow poppet valves, it is especially advantageous when used with an ultra light poppet valve, and will be described in connection therewith.
Internal combustion engine poppet valves have been commonly fabricated by machining, forging, or extruding a solid blank of high-strength, heat resistant metal, and then subjecting the blank to various finish machining and/or grinding operations. In some applications, performance requirements have made it necessary to provide a valve having a hollow stem into which a coolant, such as a sodium-potassium mixture, may be added during the fabrication process. Prior to the early 1990s, such hollow stems were formed by means such as drilling or extruding, or by forging the stem over a mandrel or a removable core, or by cold forming a tubular blank to a desired stem diameter, then shaping the fillet portion and then attaching separate cap and tip members.
A true ultra light engine poppet valve was first illustrated and described in U.S. Pat. No. 5,413,073, assigned to the assignee of the present invention and incorporated herein by reference. In the incorporated patent, the poppet valve comprises a stem element which includes an integral tip portion and a fillet portion, and a cap member which is welded to the fillet portion. Preferably, the stem including the fillet portion is fabricated by means of a deep drawing process wherein a starting blank in the form of a sheet-like disk is subjected to a plurality of cold drawing steps. The wall thickness of the stem, after the deep drawing is completed, is substantially less than that of the fillet portion or the tip portion. These steps result in an elongated flared cup wherein the outer edge of the flared fillet portion is substantially the thickness of the starting blank.
In the above-described ultra light poppet valve structure, the flared fillet region terminates in a generally radially extending edge or rim, which is received against a shoulder defined by a depression formed in the cap. The depth of the depression is approximately equal to the thickness of the fillet region. The cap is then welded to the outer edge of the flared fillet portion. Depending upon the configuration of the particular valve, the seat face of the poppet valve may be defined by either the fillet portion, or the cap member, or both.
Although the above-described poppet valve structure has proven itself to be generally satisfactory as far as fabrication and performance within the engine, it has become apparent that there are various engine applications which require an overall strength, and especially a fatigue strength, which is greater than can readily be accomplished by the above-described known and conventional method of joining the cap member to the fillet portion.